Project Summary The proposed research explores the mechanisms of Tfh dysfunction in HIV infection controlled by antiretroviral therapy (ART). The hypothesis is that Tfh are altered in ART-controlled HIV either reversibly due to transcriptional alterations or permanently due to epigenetic changes, and that evidence of this altered state or fate can be detected in peripheral blood. The work will take advantage of access to human lymph nodes, human thoracic duct lymph, and peripheral blood. Aim 1 will test whether lymph node Tfh are transcriptionally or epigenetically aberrant in ART-controlled HIV. Then, a major goal is to determine whether activated Tfh in the blood can serve as a periscope into the HIV-affected lymph node. Aim 2 will therefore use thoracic duct lymph to track a newly identified population of Tfh as they enter the peripheral blood and determine whether these cTfh contain HIV-associated molecular changes. The outcome of these studies will inform the understanding of Tfh function and HIV-associated dysfunction, define ways to measure Tfh in the peripheral blood, and provide the basis for the applicant's first R01 submission. The goal of the research strategy and training plan in this proposal is the development of the applicant's independent research career as a physician scientist. Laura Vella, MD, PhD is an Instructor in the Department of Pediatrics in the Division of Infectious Diseases at the University of Pennsylvania and The Children's Hospital of Philadelphia. To facilitate Dr. Vella's transition to independence, this proposal combines novel questions and experimental approaches with Dr. Vella's needs for scientific and professional development. Scientifically, Dr. Vella seeks to gain expertise in the biology and dysfunction of T follicular helper cells (Tfh) in HIV and to acquire skills in bioinformatic approaches to human immunology. Professionally, Dr. Vella seeks to gain experience in scientific writing, data presentation, and in the skills required to run an independent laboratory. Dr. Vella's proposed work sits at the intersection of the expertise of her mentor, Dr. E. John Wherry, and her Co-Mentor, Dr. Michael Betts. Dr. Wherry's laboratory studies the function, differentiation, and regulation of T cells in chronic infection, and Dr. Betts studies the control of HIV, with a focus on the lymph node environment. In addition to her mentors, Dr. Vella's scientific advisory committee is composed of members with expertise in HIV, Tfh, epigenetics, and patient-based research. Together, the rich scientific and collaborative environment at The University of Pennsylvania and The Children's Hospital of Philadelphia will position Dr. Vella to have a highly impactful and translational research career in human immunology, Tfh, and chronic infection.